A commercially significant fraction of air conveying ducts for modern heating, ventilating and air conditioning ("HVAC") systems is constructed of thin walled sheet metal. Flow of air or other gases through such ducts can be disturbingly noisy. Furthermore, bare metal ducts can transmit excessive amounts of heat into or out of the conveyed gas. Often it is desired to reduce the transmission of heat and noise through sheet metal air conveying ducts to conserve energy, to maintain the conveyed air within a specified temperature range, to prevent moisture from condensing on or in the duct, and to attenuate offensive noise.
One technique for reducing heat and noise emanating from sheet metal ducts involves applying an appropriate insulating material to a surface of the duct. The insulation can be placed outside the duct, but most effective sound dampening is usually achieved by insulating the interior wall of the duct. Frequently system designs call for installing thermal insulation inside ducts too.
Acoustical and thermal insulation for HVAC ducts frequently is of a web of nonwoven glass fibers in roll or sheet form. Preferably such insulation is prefabricated in semi-rigid, flat sheets of one inch or more thickness. The insulation may be laminated on one or both faces with skins of foil, mesh, paper, film and the like. The skin can provide a surface for conveniently attaching the laminate to a duct wall. It also adds somewhat to the structural integrity of the laminate. Further, a skin on the air stream face can reduce the amount of energy required to blow air through the duct. Lining rectilinear cross-section ducts with semi-rigid flat sheet insulation is generally manageable because the duct walls are also flat.
Lining a curvilinear cross-section ("curved") duct with flat sheet insulation remains problematic, however, because the insulation must distort to conform with the curvature. One traditional method of lining a curved duct is described in European Patent Application EP 0763690 A2. That method involves placing layers of insulation blankets intermediate between an outer duct and a smaller diameter, perforated tube concentric with and internal to the outer duct. The labor required to properly assemble such double wall ducts is considered unfavorably expensive.
Another technique provides self-supporting, tubular preforms molded to the curvature of selected sized ducts. The tubular preform is inserted into the duct and held in place by various attachment means. This technique suffers from the draw back that molding technology practically limits the maximum duct size for which the tubular preform can be made. It also requires that specifically sized preforms be selected to insert within given ducts.
The above-mentioned EP 0763690 A2 discloses a modern approach to lining ducts which calls for providing a plurality of parallel narrow grooves in the gas stream surfaces of flat insulation boards. The boards can be curved or bent about an axis parallel to the grooves and opposite lateral edges then can be abutted and fastened together to form a tube. The tube then can be inserted into a duct.
The gas stream surface of the grooved insulation board can be coated with a polymeric layer, however the lateral surfaces of the grooves expose uncoated insulation material. The shoulders of the grooves are designed to mate in compression when the grooved insulation board is curved. The mated shoulders of a correctly dimensioned insulation board thus would seal the exposed insulation of the lateral surfaces from the gas stream. The insulation board dimensions, e.g., thickness of board, depth of grooves, distance between grooves, must be selected perfectly to assure that the shoulders seal off the lateral surfaces. Furthermore, when such grooved insulation board is installed in flat oval ducts, the shoulders of the grooves along the flat portions do not mate.
U.S. Pat. No. 5,567,508 provides a glass fiber duct board with coated grooves. The patent discloses a method of cutting grooves into a face-coated insulation board, depositing a polymeric coating material into the grooves and then distributing the deposited material over the surfaces of the grooves with a wiper blade to coat the surfaces. Such a coated groove board would appear ideal for the utility of li ning ducts in the manner disclosed by EP 0763690. It can be readily appreciated, however, that the process for coating the grooves is quite complicated and the apparatus requires wiper blades adapted to the size and shape of the selected grooves. A simpler, more efficient method of producing an insulation board for curved ducts is desirable.
Accordingly, the present invention provides an insulation sheet comprising:
a rectangular central block of insulating material, the block having a first major dimension and a second major dimension together defining a front face and a rear face in parallel planes distant by a thickness; the block further having a plurality of grooves penetrating the front face to a floor at a depth less than the thickness and extending parallel to the second major dimension, the grooves being spaced apart from other grooves in the first major dimension direction and running the length of the second major dimension, each of the grooves having side walls which intersect with the front face to form opposing contact edges separated by a gap; and PA1 a contiguous barrier layer of an elastically deformable substance coextensive with the front face and bridging the gaps between opposing contact edges, thereby confining the insulating material of the side walls and floor of each groove to a space internal to the central block. PA1 providing a rectangular central block of insulating material, the block having a first major dimension and a second major dimension together defining a front face and a rear face in parallel planes distant by a thickness; PA1 cutting a plurality of grooves that penetrate the front face to a floor at a depth less than the thickness and extend parallel to the second major dimension, the grooves being spaced apart from other grooves in the first major dimension direction and run the length of the second major dimension, each of the grooves having side walls which intersect with the front face to form opposing contact edges separated by a gap; PA1 foaming an elastically deformable substance in a liquid; PA1 after cutting of grooves, depositing on the front face a bead of the foamed liquid along the length of the second major dimension; PA1 drawing toward the bead in the first major dimension direction a blade in contact with the front face, thereby coating the front face with foam; and PA1 devolatilizing the foam to form a contiguous barrier layer of the elastically deformable substance coextensive with the front face and bridging the gaps between opposing contact edges.
There is also provided an insulation tube that includes the above-described, novel insulation sheet which has been flexed about a groove axis parallel to the second major dimension of the central block such that the front face exhibits an approximately concave curvature viewed in a plane perpendicular to the axis.
Still further the present invention provides a duct for an air conveying utility, such as HVAC, in which the duct comprises a tubular metal case having an axis of elongation; and the novel, flexed insulation sheet inserted in the metal case.
Additionally, a novel method of making the insulation sheets of this invention has been developed. The new method comprises
The new method presents the advantage that conventional insulation sheet manufacturing equipment can be readily adapted to fabricate the novel insulation sheets. The grooves of the novel sheets are cut parallel to the second major dimension which corresponds to the cross machine direction of conventional insulation producing machinery. The barrier layer is easily applied by dispensing the elastically deformable substance in the form of foam at a leading end of the sheet and by drawing the foam over the surface of the sheet to the following end. This step can be accomplished quite simply as the sheet moves in the machine direction under a stationary doctor blade.
The present invention features insulation for the interior of a curved duct which closely conforms to the contour of the duct without distorting the insulation. Very importantly, by virtue that the barrier layer bridges the gap between side walls of the grooves, it seals off the conveyed gas stream from all underlying insulation material exposed at the side wall. This barrier effect is complete even for flat ducts sections where absence of curvature eliminates compression between opposing contact edges and does not close the gap between side walls.